This specification relates to three dimensional (3D) modeling programs, such as computer-aided design (CAD) applications used with 3D printing.
CAD software has been developed and used to generate two dimensional (2D) and 3D representations of objects. Such 3D representations of objects have employed various modeling techniques to represent the 3D object. In general, 3D models can be divided into two categories: (1) solid models that represent volumes of the object, and (2) shell models that represent the boundaries between solid and non-solid parts of the 3D object. Traditionally, CAD software has focused on surface only representations, e.g., boundary representation (BREP), which are techniques that use various forms of surface discretization, such as polygonal meshes, parametric volumes or surfaces, such as nonuniform rational B-splines (NURBs), subdivision surfaces, etc. Volumetric representations have included voxel structures for the purpose of describing inherently volumetric objects, such as human body parts as scanned by Magnetic Resonance Imaging (MRI) and Computerized Axial Tomography (CAT) machines.